Sucralose, 4,1′,6′-trichloro-4,1′,6′-trideoxygalactosucrose, a sweetener with a sweetness intensity several hundred times that of sucrose, is made from sucrose by replacing the hydroxyl groups in the 4,1′, and 6′ positions with chlorine. Synthesis of sucralose is technically challenging because of the need to selectively replace specific hydroxyl groups with chlorine atoms, while preserving other hydroxyl groups including a highly reactive primary hydroxyl group. Numerous approaches to this synthesis have been developed. See, e.g. U.S. Pat. Nos. 4,362,869, 4,826,962, 4,980,463, and 5,141,860, which are expressly incorporated herein by reference.
Crystallization is widely used to purify and recover compounds, including, but not limited to, sugar, sucralose, and related substances. Crystallization is carried out by inducing the formation of crystals in a solution, followed by separating the crystals from the remaining solution (the “mother liquor”), i.e., recovering the crystals.
Sucralose typically crystallizes from water as needle-shaped crystals, as described for example in U.S. Pat. Nos. 4,343,934, 5,136,031, 4,980,463, 4,977,254, 5,530,106, 5,498,709, and 4,950,746. Many of these crystals typically have a length-to-diameter (L/D) ratio ranging from about 4:1 to about 10:1, and in some cases even higher. Indeed, all previously known crystallization processes of which the applicants are aware produce needles of this type. Typically, many such needles are broken, which produces undesirable dust. Nonetheless, at least a significant fraction of the needles remain that have high L/D values. Such crystalline sucralose has poor handling characteristics, including poor flow, which makes it difficult to incorporate into formulations with other ingredients.
Attempts to overcome these difficulties have been reported in the patent literature. For example, U.S. Pat. No. 5,932,720 to Sankey discloses a method for increasing the flowability of crystalline sucralose by treating the crystalline material in a fluidized bed at ambient temperature with additions of water, followed by a fluidized drying phase.
In U.S. Pat. No. 4,918,182 to Jackson et al, there is disclosed crystalline sucralose said to have a mean particle size of at most 10 microns (with 5 microns preferred), the maximum particle size being no more than twice the mean (preferably at most 10 microns). This product is said to exhibit enhanced stability to heat. A method of enhancing the thermal stability of crystalline sucralose is also disclosed, comprising jet milling the sucralose to reduce the particle size, and render the size distribution such that the maximum size is no more than twice the mean.
Notwithstanding the foregoing, there remains a need for stable sucralose crystals that have good flowability characteristics, preferably not requiring post-crystallization processes to modify the crystal shape.